Answer: Often, when fruits are undersized and/or rot or drop off when they are small, it is an indication of poor pollination. Watermelon flowers are pollinated by bees, and if there aren't bees around to do the pollinating, you might have to do it by hand. Simply transfer pollen to the female flower.
Other problems include not enough water, inadequate nutrient levels, or disease. However, if the plants look lush and healthy, I'd suspect pollination problems.
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